The invention discloses a toxic and harmful gas detection system based on a multi-rotor unmanned aerial vehicle platform. A toxic and harmful gas detection module carried on a multi-rotor unmanned aerial vehicle is used for detecting toxic and harmful gas in a target area, a high-definition camera is used for acquiring real-time video images in the target area, an onboard GPS (global positioning system) and a fixed-height air pressure gauge are used for acquiring the spatial position of the target area, and all acquired data are analyzed and integrated. On one hand, security data can be provided for sudden event site emergency disposal personnel; on the other hand, evidence materials can be provided for law enforcement and discovery of environmental pollution caused by stealing emission and discharge, and the requirements of sudden event site toxic and harmful gas emergency monitoring, discovery of environmental pollution caused by stealing emission and discharge and the like can be met.